A vigorous shallow earthquake sequence along the southern coast of Puerto Rico commenced on 28 December 2019 in a region with little prior large seismicity. The largest event in the sequence (
The Puerto Rico–Virgin Islands (PRVI) block lies within the Northern Caribbean Plate Boundary Zone—a zone accommodating stresses between the larger North America and Caribbean plates. Data from Global Positioning System (GPS) sites throughout the PRVI block have been used to confirm the existence of a distinct microblock in the southwest. It is no coincidence that this portion of the PRVI block is the epicentral region of the 7 January 2020 Mw 6.4 earthquake and the ensuing seismic sequence. Prior to the mainshock, the southwestern Puerto Rico (SWPR) region exhibited most of the onland seismic activity. The 2020–2021 SWPR earthquake seismic sequence has been characterized by having an atypical aftershock decay distribution occurring along multiple faults. As a result, fault parameters of the 7 January 2020 mainshock have been poorly defined by conventional seismic methods. Here, we present results from campaign and continuous GPS sites in SWPR, and compare GPS-derived displacements to those computed from the U.S. Geological Survey National Earthquake Information Center (NEIC) focal mechanism. We conclude that irrespective of which nodal plane is used, the observed coseismic displacements from GPS differ from those predicted using a simple elastic model and the NEIC focal mechanism. We infer based on these observations that the complex mainshock rupture resulted in a suboptimal double-couple solution.
more » « less- Award ID(s):
- 2022264
- NSF-PAR ID:
- 10497891
- Publisher / Repository:
- Seismological Society of America
- Date Published:
- Journal Name:
- Bulletin of the Seismological Society of America
- Volume:
- 113
- Issue:
- 1
- ISSN:
- 0037-1106
- Page Range / eLocation ID:
- 99 to 114
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract M W = 6.4), struck on 7 January 2020 and involved normal faulting. It produced extensive damage in southern Puerto Rico and power disruption across the island. Nearby strong ground motions and static offsets from GPS stations along with teleseismic recordings are inverted for the kinematic rupture process of the mainshock. The ~15‐km‐long rupture is spatially concentrated, with most slip between 3 and 13 km deep and peak slip of ~1.6 m. The static stress drop is high, ~19 MPa, with the rupture locating in the eastern section of a ~30‐km‐long band of seismicity bisected by a near‐orthogonal lineation. Complex faulting and high stress in the intraplate region appears to be responsible for the high earthquake productivity. -
Abstract The recent Indios, Puerto Rico earthquake sequence has drawn attention, as the increased seismicity rate in this area was unprecedented. The sequence began on 28 December 2019, caused a 6.4 magnitude earthquake on 7 January 2020, and remained active over a year later. This sequence fits the nominal definition of an earthquake swarm in that it had an abrupt onset, a sustained high rate of seismicity without a clear triggering mainshock or evidence for Omori decay, and a lack of adherence to Bath’s law. However, the sequence also had several prominent mainshock–aftershock (MS–AS) sequences embedded within it. We applied three-station waveform cross correlation to the early part of this sequence using the Puerto Rico Seismic Network (PRSN) catalog as templates, which confirmed the mixture of swarm and MS–AS patterns. In an effort to place this intriguing sequence in the context of the previous seismicity in Puerto Rico, we investigated the existence of swarms and MS–AS sequences recorded by the PRSN since 1987 by identifying sequences with increased seismicity rate when compared to the background rate. About 59 sequences were manually verified and characterized into swarms or MS–AS. We found that 58% of the sequences follow traditional swarm patterns and 14% adhere to traditional MS–AS behavior, whereas 29% of the sequences have a mixture of both swarm and MS–AS behaviors. These findings suggest that it is not unusual for the Indios sequence to have a mixture of both the characteristics. In addition, the detection of many swarms distributed over a broad area of the subduction interface indicates stress heterogeneity and low-coupling consistent with prior studies indicating that the potential for a magnitude ∼8 megathrust earthquake along the Puerto Rico trench is unlikely.more » « less
-
more » « less
Abstract The heterogeneous seafloor topography of the Nazca Plate as it enters the Ecuador subduction zone provides an opportunity to document the influence of seafloor roughness on slip behavior and megathrust rupture. The 2016 Mw7.8 Pedernales Ecuador earthquake was followed by a rich and active postseismic sequence. An internationally coordinated rapid response effort installed a temporary seismic network to densify coastal stations of the permanent Ecuadorian national seismic network. A combination of 82 onshore short and intermediate period and broadband seismic stations and six ocean bottom seismometers recorded the postseismic Pedernales sequence for over a year after the mainshock. A robust earthquake catalog combined with calibrated relocations for a subset of magnitude ≥4 earthquakes shows pronounced spatial and temporal clustering. A range of slip behavior accommodates postseismic deformation including earthquakes, slow slip events, and earthquake swarms. Models of plate coupling and the consistency of earthquake clustering and slip behavior through multiple seismic cycles reveal a segmented subduction zone primarily controlled by subducted seafloor topography, accreted terranes, and inherited structure. The 2016 Pedernales mainshock triggered moderate to strong earthquakes (5 ≤ M ≤ 7) and earthquake swarms north of the mainshock rupture close to the epicenter of the 1906 Mw8.8 earthquake and in the segment of the subduction zone that ruptured in 1958 in a Mw7.7 earthquake.
-
On January 7, 2020, the southwest of Puerto Rico was struck by a M6.4 earthquake that caused the collapse of several structures, including a 3-floor operational reinforced concrete school. While it is well known that the island is located on an active seismic zone, this event took by surprise and unprepared the affected communities, as the last significant earthquake dated 1918 and most attention in the island is directed towards recurrent tropical cyclones hazards. This event offers a unique opportunity to promulgate an earthquake awareness culture in the community and promote earthquake engineering within our students. This paper presents an undergraduate research case study where the students designed a vertical evacuation structure for a coastal community in Mayaguez, PR. The group was comprised of undergraduate students with different academic background: civil engineering, surveying and architecture. The objective was to foster interdisciplinary problem-solving skills and advance the knowledge of earthquake engineering principles in the students. The results from the project proved that when students from different background and perspectives work together, the solutions that arise are holistic and the knowledge acquired is deeper and better rounded.more » « less
-
FAST deployed from 8-12 January 2020, documenting the performance of 61 structures located in six different cities along the southwestern coast of Puerto Rico between the cities of Ponce and Mayagüez. A variety of structure types are surveyed, including residential building structures and bridge infrastructures. FAST collected perishable data through the Fulcrum app by completing damage assessment forms, recording high-resolution overall and detailed images of observed damages, and notes summarizing key observations. Fieldwork data collection is conducted according to the StEER’s FAST handbook.This project encompasses the products of StEER's Level 2 response to the Puerto Rico Earthquake from December 2019 to January 2020. The main event, a Mw 6.4 quake, occurred on January 7th, accompanied by numerous aftershocks. The governor reported one casualty and eight injuries, declaring a State of Emergency. The earthquakes damaged 10,000+ structures, collapsing 80, predominantly residential units. Infrastructure, bridges, and roads were also affected, leaving two-thirds of the island without power. Over 8,000 people were displaced to shelters, while 63,000 received assistance, with FEMA handling over 13,852 aid requests. In response, the StEER conducted a post-earthquake performance assessment from 8-12 January 2020, documenting the performance of 60 structures located in six different cities along the southwestern coast of Puerto Rico. The field data collection focused on acquiring high-resolution photographs and notes on structural performance necessary to construct detailed case studies of each structure.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1785/0120220115
